Large amounts of expensive high hardness, high strength, and high impact toughness military steels are used for purposes such as bunker buster bombs, missiles, tank bodies and aircraft landing gears.
Eglin Steel (U.S. Pat. No. 7,537,727, incorporated by reference) was a joint effort of the US Air Force and Ellwood National Forge Company program to develop a low cost replacement for the expensive high strength and high toughness steels, AF-1410, Aermet-100, HY-180, and HP9-4-20/30. One application of Eglin steel was the new bunker buster bombs, e.g. the Massive Ordnance Penetrator and the improved version of the GBU-28 bomb known as EGBU-28.
High strength is required to survive the high impact speeds that occur during deep penetration. Eglin steel was planned for a wide range of other applications, from missile and tank bodies to machine parts.
One shortcoming of Eglin steel is its limited mechanical properties for large manufactured products which are as follows:                Hardness (HRC), up to C48        Ultimate tensile strength (UTS), up to 250 ksi        Yield strength (YS) up to 210 ksi        
Another shortcoming of Eglin steel is that its structural performance during impact tests of large articles, such as bunker buster bombs, vary somewhat below the impact test results of smaller laboratory products. The discrepancies in results are due to difficulties with heat treating of Eglin steel.
The present invention overcomes the shortcomings of Eglin steel by providing a steel that has higher mechanical properties and consistent results from chemical composition and heat treating. The improved steel has a medium carbon content, low nickel, molybdenum, and tungsten contents, and the strong carbide forming elements vanadium and titanium or niobium. The new alloying concentrations of vanadium, titanium or niobium, and tungsten affect the conditions of melting, processing, and heat treatment and as a result, it's higher mechanical properties.
One benefit of the new steel is higher performances of armor plate, deep penetrating bombs and missiles. Another benefit is that, at the same performance, less steel is required to match the performance of Eglin steel.
Another benefit of the invention is smaller amounts are required of the expensive elements nickel (Ni) and tungsten (W). The invention requires about 0.1 to less than 3.0% wt. of Ni and about 0.1 to 2.0% wt. of W, versus at most 5 max % wt. of Ni and 3.25 max % wt. of W for Eglin Steel.